Bioethanol is becoming more widespread as an alternative fuel to petroleum. Bioethanol is mainly manufactured by the saccharification and fermentation of sugar cane or maize. In recent years, techniques have been developed for manufacturing bioethanol from wood-based or plant-based biomass (also known as cellulose-based biomass), including the unused portions of crops such as waste wood or rice straw, which are not in competition for use as foodstuffs or animal feed.
In order to use a cellulose-based biomass as a raw material, and enable the manufacture of bioethanol using a conventional ethanol fermentation method, the cellulose must be saccharified. Examples of the saccharification method include a concentrated sulfuric acid saccharification method, a dilute sulfuric acid-enzymatic saccharification method, and a heated water saccharification method, but many problems still remain to manufacturing bioethanol inexpensively.
On the other hand, another method exists in which the cellulose-based biomass is converted to a mixed gas containing hydrogen and carbon monoxide, and ethanol is then synthesized from this mixed gas. With this method, tests are being conducted with the aim of manufacturing bioethanol efficiently from cellulose-based biomass that is difficult to use in the ethanol fermentation method. This method is not limited to wood-based and plant-based biomass, but can use all manner of organic matter as the raw material, such as animal-based biomass derived from animal corpses and feces; biomass derived from raw garbage, waste paper and waste fiber; and plastic.
Moreover, the mixed gas of hydrogen and carbon monoxide can also be obtained from resources besides petroleum, including natural gas and coal, and therefore methods of synthesizing C2 oxygenates, such as ethanol, acetaldehyde and acetic acid, from this type of mixed gas are also being researched as potential techniques for breaking away from petroleum dependency.
Examples of known methods for obtaining C2 oxygenates from a mixed gas of hydrogen and carbon monoxide include methods in which, for example, the mixed gas is brought into contact with a catalyst in which rhodium and an alkali metal are supported on a silica gel carrier (for example, see Patent Documents 1 and 2).